The present invention is directed generally to variable spacing probing tips and more particularly to an attachable/detachable variable spacing probing tip system for a measurement probe where the variable spacing probing tips are attachable and detachable from the measurement probe.
Variable spacing probing tip adapters have been used for many years with differential measurement probes. U.S. Pat. No. 6,400,167 describes two versions of variable spacing probing tip adapters for differential probes. The first adapter is referred to as a Longhorn Adapter, manufactured and sold by Tektronix, Inc., Beaverton, Oreg., under Part No. 016-1780-00 and used with the P6200 family of differential probes sold by Tektronix, Inc. The P6200 family of differential probes has a measurement probe head with dual socket type probing tips extending from the nose of the probe head. The Longhorn adapter has offset probing tips that are ganged together with an insulating material, such as plastic or the like. The ganged probing tips each have a contact shaft extending from the insulating material with a pitch geometry of the contact shafts compatible with the socket type probing tips. Below the insulating material, the probing tips have bends formed in them to offset the probing tips which allow the probing tips to rotate to match various pitch geometries of probing points on a device under test.
The other version of the variable spacing probing adapter is also sold by Tektronix, Inc. under Part No. 016-1885-00 and used with the P6330, P7330 and P7350 differential probes. These differential probes have a probe head with probing tips extending from the nose of the probing head. The variable spacing probing adapter has a holder with a cavity at one end and bores extending from the cavity to the front of the holder. The bores have a pitch geometry that matches the pitch geometry of the probing tips extending from the nose of the probing head. Probe point elements are disposed in the bores of the holder with one end exposed in the holder cavity and the other end extending from the end of the holder. The ends of the probe point elements exposed within the cavity have a bore formed therein that is filled with a conductive elastomer material. The ends of the probing point elements extending from the end of the holder are angled and tapered to a point to form angled probing tips. The holder is positioned over the probe head nose with the probing tips in the nose puncturing the electrically conductive elastomer in the respective bores of the probe point elements. The angled probing tips of the probe point elements are rotatable within the holder to allow the probing tips to be matched to the various pitch geometries of the probing points on the device under test.
As the bandwidth of measurement instruments, such as oscilloscopes and the like, increases, there is a corresponding need for measurement probes having equal or greater bandwidths. A drawback to the above described probing tip adapters is the effects of probe tip capacitance and inductance on the overall bandwidth of the probe. The additional lead length produced by the probing tips of the probing tip adapters increases the overall capacitance and inductance of the probing tips which degrades the overall bandwidth of the probe. One solution to this problem is to separate the probing tips from the active circuitry in the probing head of the measurement probe. U.S. Pat. No. 6,704,670 describes a wideband active probing system where the probing tip or tips of the probe are separable from a probe amplifier unit. One or more probe cables are connected to a probe tip unit which are connected to the probe amplifier unit for conveying signals received by a probe unit. Various types of probe tip units may be connected to the probe amplifier unit. The probe tip unit may contain circuitry ranging from conductor traces to various resistive, capacitive, and/or other electronic elements. An advantage of such a probe design is that it allows the placement of the substantially smaller probe tip unit onto difficult to reach contacts on a device under test instead of a larger measurement probe containing probe amplifier circuitry.
One type of probe tip unit for the wideband active probing system is a differential probe unit. The differential probe unit includes a probe unit housing and probe assemblies. Each probe assembly includes a probe barrel, a probe barrel nose cone and a probing tip. The center conductor of the probe cable is electrically coupled to the probing tip and an outer shielding conductor of the probe cable is electrically coupled to the probe barrel. The probe barrels are partially disposed within the probe housing with the probe barrel nose cones attached to the respective probe barrels extending outward from the probe housing. The probing tips extend partially out of the respective probe barrel nose cones. The longitudinal axis of each probe barrel nose cone is offset at an angle from the longitudinal axis of its respective probe barrel. The probe barrels are rotatable within the probe unit housing. This allows the probing tips to be rotated to various separation distances to match the separation distances of probe points on a device under test. The differential probe unit further includes elastic compressible elements that allow the probe assemblies to move along the longitudinal axis of the probe barrels for mating with probe points of differing heights on the device under test.
While the commercial implementation of the above described wideband active probing system provides a 7 GHz bandwidth, the future of measurement instruments and probes is for higher and higher bandwidth capability. This will require reducing the capacitive and inductive effects of the probing tips below what is capable with existing variable spacing differential probes. What is needed is a variable spacing differential probing tip system that provides greater bandwidth than existing variable spacing differential probing solutions. The variable spacing differential probing system should be compact to allow probing of fine pitched probing points on a device under test while at the same time allowing ease of adjustment of the probe spacing. The variable spacing differential probing tip system should also be attachable and detachable from the measurement probe to allow for a variety of probing tip solutions for the same measurement probe.